During enamel development, an extracellular matrix is secreted by the ameloblasts. The amelogenin proteins are the principle organic constituent of this matrix, and these proteins are thought to be involved in regulation of size and growth of enamel crystals. The amino acid sequence of the amelogenin proteins is conserved in divergent species, perhaps to preserve the protein structure in order to provide a specific function during enamel formation or maturation. since most of the amelogenin protein is not present in mature enamel, it is likely that proteolytic degradation occurs as mineral forms. The amelogenin proteins that are extracted from developing teeth therefore represent a mixture of newly synthesized and partially degraded proteins. In this proposal we describe experiments designed to study amelogenin expression at the level of mRNA. The bovine X-chromosomal primary transcript is alternatively spliced, and we propose to evaluate levels of the 4 mRNAs so far identified. We will also study levels of the bovine Y-chromosomal mRNA, and search for additional alternative splice products. Isolation of the bovine Y-chromosomal amelogenin gene will allow us to verify the sequence of the Y-linked cDNA obtained by PCR, and to compare gene structure to that of the X-chromosomal gene. In addition, we plan to evaluate certain human odontogenic tumors for expression of amelogenin mRNA, in order to clone human cDNAs to determine whether the human Y-linked gene is active and whether alternative splicing occurs also in humans.